1. Field of the Invention
This invention relates to novel alprenolol derivatives for improving the so-called bioavailability of alprenolol as a .beta.-blocking agent.
2. Description of the Prior Art
When alprenolol which is used as a .beta.-blocking agent is orally administered, it has been known that the bioavailability of alprenolol in vivo is lowered because of being subjected to the first-pass effect of the liver similarly to other medicines. For example, it has been reported that the bioavailability of alprenolol is only 15% in the oral administration. Therefore, there is a problem that the concentration of alprenolol in blood is difficult to control.
It has been known that chemical modification as a means for preparing prodrug of the medicines. The method, however, has been intended to improve absorption of the medicines from gastrointestine [Clayton J. P. et al., J. Medicinal Chem., 18 (2), 172 (1975)] and is not a prodrug preparation to avoid the first-pass effect of the liver. The preparation of prodrug to evade the first-pass effect of the liver has not yet been reported of course on alprenolol, and on other various medicines.